508 FLIGHT MAY 9, 1935.
FLYING ON 250 c.c.
Villiers Two-stroke Motor Cycle Unit as " Occasional Engine " for a
Sailplane : The Outcome of a Startling but Practical Scheme
Conceived by Sir John Carden
Puzzle—find the power unit J No one would suspect that an auxiliary engine is tucked away within the fuselage of the Carden-
Baynes sailplane.
SEVERAL attempts have been made from time to time to combine the glider or sailplane and the power-driven type of aircraft in one machine. Many of the ultra-light
'planes which took part in the Lympne competitions some
years ago were virtually gliders with small motor cycle engines
fitted. Although these machines were remarkably efficient,
regarded as aeroplanes, they did not achieve L/D ratios com
parable with those which the modern type of sailplane attains.
The very fact that the engine and airscrew were exposed to the
airstream increased the drag very materially and reduced the
efficiency from the sailplane point of view.
With a pure and simple glider, on the other hand, a very
high L/D ratio is achieved by having a very large wing span,
so as to obtain low span loading with consequently low in
duced drag. To get into the air such a machine must, how
ever, be launched either by a ground crew catapulting it off by
means of rubber cords, or by towing behind a motor car or an
aeroplane. It is often possible, if a height of some hundreds of
feet can be attained initially, for such a machine to reach a
region where strong up-currents exist, and by making use of
these the pilot can often make cross-country flights of con
siderable duration.
If the sailplane gets out of one up-current, however, it may
not be able to reach another before it has lost too much height,
and will then have to land. In most cases this means that the
pilot has to telephone back to his starting point, and a car
with a trailer has to be sent out to find him and bring him
back. All this is something of a handicap to the sailplane
pilot, and if means can be found to enable
him to regain his base without outside
assistance his independence would be
vastly increased, and, moreover, he
would probably be able to put in many
more flights in the course of a day.
Sir John V. Carden, who has been a
keen amateur pilot for a good many
years, and who has owned several aero
planes (his present mount is a Miles
"Hawk"), has had the brilliant idea
of utilising an " occasional " power
plant; in other words, his engine is
ordinarily mounted in a position out of
the airstream; but when it is wanted,
either to get the sailplane off the ground
initially, or for reaching a region of up-
currents, it can be put into operating
position and started, the machine then
proceeding as an ordinary low-power
aeroplane.
It might have been thought that to
do this would have been a very difficult
task. Sir John has, however, schemed
out an amazingly neat and simple
method. In his work he has had
the whole-hearted co-operation of Mr. L. E. Baynes, the de
signer of the very successful " Scud " sailplanes, and of the
Villiers Engineering Co., Ltd. Mr. Baynes has designed for
this extremely interesting development a new high-efficiency
sailplane which has been constructed at the Abbott Motor
Works, Wrecclesham, Surrey, where Flight last week had an
opportunity of inspecting the new craft.
Engine Reliability
The engine which Sir John Carden is using is a single-cylinder
Villiers two-stroke of 249 c.c. capacity. In its normal form
ihis engine is, of course, an ordinary motor cycle engine with
its cylinder pointing upwards. For the sailplane it was de
sired to invert the engine, since by doing this the centre of the
crankshaft would be raised, thus giving the necessary airscrew
clearance with very small overall height. The Villiers Com
pany very sportingly undertook the work of converting tht
engine, and the tests which Sir John has had carried out at
Wrecclesham have been extremely satisfactory; the engine has
run for many hours on end at full throttle without any troubk
and without any signs of overheating, the cowling being so
arranged that it forms a venturi, while the airscrew blades
passing close behind the cylinder help to produce a very strong
air current.
The mounting of the engine p very simple. Two tubes
having a diagonal bracing member run to the crank case and
vee tubes to the cylinder head, so that the whole system is
perfectly triangulated and a very rigid mounting provided.
The Carden engine mounting. 0"
the left may be seen the details,
while the right-hand view shows
the engine in an intermediate
position. The cowling has been
removed to show the mounting
structure. (Flight photograph*)